Lately, various kinds of navigation assisting devices have been developed in terms of collision prevention and human life safety of ships. As such a navigation assisting device, a radar apparatus provided with a TT (Target Tracking) function is known, for example. The TT function is to detect positions and velocity vectors of the target objects which exist around a ship concerned based on a transition of radar images of the past, and inform of the target objects with risks, etc. The TT function is conventionally referred to as an “ARPA (Automatic Radar Plotting Aid).”
Conventionally, the radar apparatus provided with the TT function as described above may be configured to output the data indicating the position, speed, course and the like of the target object detected by the TT function (hereinafter, may be referred to as “target object data”) to the outside of the apparatus. Because the target object data is updated every moment, it is preferred that new target object data can be outputted each time without any delay if it is configured so that the target object data is outputted to the outside of the apparatus.
For the output of the target object data to the outside as described above, the international standard defines a serial output which is carried out at a predetermined communication rate. The communication rate defined by the international standard may not be fast enough, and if many target objects are detected by the TT, there is a problem that it takes a lot of time to finish the output of all the target object data. Thus, if the output of the target object data takes time, a delay will occur to output the subsequent new target object data.
However, because the TT processes the radar image to detect the target object, it has a limitation in the number of detectable target objects due to a high load of the processing operation. Therefore, although the delay of the data output occurs if there are many target objects, this does not directly mean that a large delay to cause practical problems has occurred.
In the meantime, AISs (Universal Shipborne Automatic Identification Systems) have become common in recent years, and radar apparatuses which can use both the information of the AIS and the information acquired by the TT function have appeared in the market. The AIS is a system for transmitting positional information, traveling information and the like on a ship concerned to the circumference by wireless communications at a predetermined cycle according to the status of the ship (mooring, traveling, etc.), and it can acquire information on the positions, speeds and the like of other ships by receiving the positional information, traveling information and the like from the other ships (the target object data, described above).
The radar apparatus which can use both the information of the AIS and the TT (ARPA) is disclosed in JP 2008-281504(A), for example. Further, the processing of the received AIS information is disclosed in JP 3,995,462, for example.
Because the radar apparatuses which can deal with the multiple information of the AIS and the TT as described above have been developed, it is desired that the target object data based on the AIS is also outputted to the outside of the radar apparatus, in addition to the target object data based on the TT.
In the meantime, because the AIS acquires all the target object data transmitted from other ships as long as they are receivable, the radar apparatus side which received the outputs must treat a more amount of the target object data comparing with the TT. For this reason, in the radar apparatus which can use the information of both the AIS and the TT, the total number of the target object data to treat may increase significantly. In this case, if the apparatus is configured to output all the target object data to the outside, the data amount to be outputted increases in proportion to the number of the target objects. Therefore, the output cycle of the target object data will be very long, and a large delay to the data update occurs on the side of an instrument which receives the target object data, resulting in a practical problem.